Press fitting of slightly larger diameter valve guides into smaller diameter cylindrical counterbores contained in internal combustion engine heads is required to form a very stable fit between the two components, so that loosening is prevented and heat transfer is facilitated during operation of the engine. In the past, various surface textures and techniques have been used to facilitate press fitting of valve guides into internal combustion engine heads. For example, industrial specifications have required external surface textures for guide valves of 32 microinches maximum and 64 microinches maximum, respectively. No minimum surface texture is set forth in either specification. Valve guides having such above described surface textures are subsequently coated with an oil-containing coating that includes a lubricating oil so that press fitting of the valve guide into the engine head proceeds without seizing and/or galling. Phosphate coatings are typically used for this purpose. The present invention utilizes a roughened surface coating on the external surface of the valve guide that is capable of containing a sufficient amount of light lubricating oil to avoid the need for such oil-containing coatings.
Another industrial specification for valve guides requires an external surface texture of from 40 to 100 microinches. Valve guides manufactured under such specification are intended to be coated with a lubricating oil and then press fit into an engine head. It has been discovered by the present invention that such specification should be tightened to require external valve guide surfaces having a roughened surface from about 50 to about 100 microinches because the use of surface textures below about 50 microinches does not permit sufficient amounts of lubricating oil to be contained by the external surface to ensure that press fitting will proceed smoothly.
By way of further background, U.S. Pat. Nos. 4,896,638; 3,384,515; 3,828,415; 3,258,838; and 4,342,293 illustrate various manufacturing techniques for fabricating various engine components. U.S. Pat. No. 5,190,002 illustrates the use of certain surface textures for an engine valve that is sufficiently smooth to cause minimal wear during contact with other engine parts but also sufficiently rough to contain lubricating oils.